Improved cyanide copper plating baths



United States Patent INIPROVED CYANmE COPPER PLATlNG BATHS Fred I. Nobel, North Valley Stream, and Barnet D. Ostrow, North Bellmore, N.Y.

N Drawing. Application January 30, 1956 Serial No. 561,992

10 Claims. (Cl. 204-44) The present invention is directed to alkaline cyanide plating baths for depositing copper and brass, and more particularly to high efficiencybaths for producing bright deposits. l

It has been recognized for a considerable time that low concentration baths containing copper cyanide have a limited plating range and low cathode efiiciency for producing commercially useful deposits. To overcome such disadvantages, high efiiciency plating baths were developed which operated with very high concentrations of copper cyanide and with the presence of sodium cyanide. A typical bath of this kind is listed as A in the following table, the constituents being in ounces per gallon:

NaGNS Cetyl Betaine 0.05 0.05 Rochelle Salt. 6. Temperature, "F 160-170 160-170 150-160 O.D. Range, a.s.f 10-40 10-40 0-40 Sodium salts were employed in composition A because they are less costly than potassium salts; for example, .the cost of potassium cyanide is from 2 to 3 times that of sodium cyanide. This formulation had several disadvantages. Because of the high concentration of copper cyanide the drag-out was considerable and the initial investment in chemicals was quite high.- The bath also formed carbonates as breakdown products of sodium cyanide, which narrowed the plating range. This necessitated the periodic precipitation of the carbonates by soluble salts of calcium or barium, causing interruption of the plating operation.

To overcome the disadvantages of the sodium bath, it was proposed to use potassium and such aformulation is listed at B in the above table. Another such' bath and containing Rochelle salt is listed at C in said table. These baths had the advantage that the concentration of copper cyanide was one half of that used in the sodium containing bath to achieve the same results. Because of the lower metal content the drag-out was reduced. I

All of the aforementioned baths tended to keep the free potassium or sodium cyanide as low as possible, because with low free cyanide the cathode efiiciencywas measurably improved. They required a high cathode efliciency (close to 100%) to produce bright deposits, as increase of free cyanide over the optimum tended to reduce the bright plating range and to give burned deposits. However, such lower free cyanide concentrations had an adverse eifect on anode corrosion, particularly in older baths high in carbonate and iron, resulting in roughness of the deposit. Raising the free cyanide would assist in increasing anode corrosion but this could not be done because of the adverse efiect on efiiciency of operation and brightness of deposit.

2,891,896 Patented June 23, 1959 The present invention is intended and adapted to overcome the difiiculties and disadvantages inherent in the prior art, it being among the objects thereof to produce deposits of copper and brass from cyanide solutions at high current densities and at high efficiencies.

Y It is also among the objects of the invention to produce such deposits from baths which are more economical than those heretofore described and used in the art.

It is further among the objects of the invention to pro- .vide a bath which permits the operation of copper and brass platingbaths over a wide range of free cyanide concentration and in which the bright current density plating range is materially widened.

In accordance with the present invention, there is introduced into cyanide copper and brass plating baths a soluble compound containing the nitrate, nitrite or nitroso radical, whereby all the shortcomings and deficiencies of the aforementioned baths are overcome.

It permits the doubling and, in many cases, the tripling of the allowable current density without adverse eifects, Also, the free cyanide content of the bath may be varied over a wide range of concentrations without impairing the plating characteristics of the bath. Both inorganic and organic example 2-nitro-1-butanol, 2,4-dinitrobenzene sulfonic acid potassium salt, nitrobenzoic acid sodium salt, S-nitrosalicyclic acid potassium salt, 1-nitroso-2-naphthol-3,6- disulfonic acid sodium salt,-and p-nitrosophenol sodium salt. 'It is necessary that the additive be soluble in the bath and in the above stated ratios. With lower ratios good cathode characteristics are still obtained but there may be an adverse eifect on anode corrosion. On the other hand, higher ratios do'not give the'full advantages of increased current 'density range and latitude of free The following are specific examples of the operation of the present invention, the amounts of the constituents being given in ounces per gallon:

Example 1 Bath A operated in a Hull cell at 2 amperes for five minutes at F. with agitation showed a bright plating range of 10-40 amperes per square foot. A similar bath was prepared in which the copper cyanide concentration was the same as that of bath B, and it had the following composition:

Copper cyanide '8.0 Sodium cyanide 9.8 Free sodium cyanide 1.0 Sodium hydroxide 4.0 Cetyl betaine 0.05 NaCNS 0.75

When operated in a Hull cell at 2 a.s.f. for five minutes at 170 F. with agitation it showed a bright plating range of 5.2O a.s.f. To this bath there was added 2 ounces per gallon of N0 in the form of sodium nitrate and the bath was operated under the same conditions. The bright plating range was 10 70 a.s.f.

By the present invention, a bath using sodium, salts can give plating characteristics at least equal to a similar bath having twice the copper cyanide concentration, and

give the same characteristics as an equivalent potassium bath.

Example 2 Bath A was modified by the addition of ammonium nitrate and had the following composition:

Copper cyanide 16.0 Sodium cyanide 18.6 Free sodium cyanide 1.0 Sodium hydroxide 4.0 Cetyl betaine 0.07 NaCNS 2.0 NH NO 5.0

The addition of the nitrate ion increased the current density range of 10-40 a.s.f. to 10-100 a.s.f.

Example 3 To bath A there was added 3 ounces per gallon of po tassium nitrite and operated as described in Example 1. The current density range was increased to 10-100 a.s.f.

Example 4 A standard low efiiciency bath containing Rochelle salt had the following composition:

Copper cyanide 3.5 Sodium cyanide 4.6

Free sodium cyanide 0.75 Sodium carbonate 4.0 Rochelle salt 6.0

It was operated at 150 F. at 2 a.s.f. with agitation. A smooth deposit was obtained in the current density range of 15-50 a.s.f.

To the bath was added 1 ounce per gallon of 2,4- dinitrobenzene sulfonic acid potassium salt, and it was operated under the same conditions. A smooth deposit was obtained in the current density range of 15-80 a.s.f. and the cathode appearance was improved.

Example 5 A high efiiciency Rochelle salt bath having the following composition was prepared:

Copper cyanide 6.0 Potassium cyanide 9.6 Potassium hydroxide 2.0 Free potassium cyanide 1.2 Rochelle salt 6.0

The bath was operated in a Hull cell at 2 a.s.f. at a temperature of 160 F. with agitation. The plating range was O-50 a.s.f. Upon the addition of 3.5 ounces per gallon of potassium nitrite, the plating range was increased to 0-100 a.s.f.

Example 6 A bright copper plating bath containing selenium had the following composition:

Copper cyanide 10.0 Sodium cyanide 12.0 Free sodium cyanide 1.0 Rochelle salt 6.0 Sodium hydroxide 3.0

Se as selenourea .0004

4 (c) To the original composition there was added 3 ounces per gallon of sodium cyanide. The bright plating range was reduced to 0-25 a.s.f. Upon the addition of 6 ounces per gallon of sodium nitrate the bright plating range of 0-100 a.s.f. was obtained.

Example 7 To the standard high eflrciency bath of Example 5, there was added 1-nitroso2-naphthol-3,6-disulfonic acid sodium salt in the amount of 2 ounces per gallon. The plating range was increased to O- a.s.f.

The above examples show that the incorporation of compounds containing N0 N0 and NO radicals in copper plating baths introduces the ability to operate satisfactorily with high free cyanide and high carbonate contents. Considerable economies are obtained in the chemical constituents of the bath because of the improvement in the plating range, permitting results to be obtained which are equivalent to those obtained with all-potassium formulations. Such an improvement is particularly effective in cyanide brass plating baths, especially in high speed baths where it is important to control the ratio of copper to the nitro compounds within the above described limits.

Example 8 In co-pending application Serial No. 521,392 entitled Process for Plating Bright Brass, now Patent 2,817,627, there is described a composition which results in substantial improvement in brightness of deposit and increase of bright plating range. By the present invention it becomes possible to reduce the copper concentration similarly to copper plating baths and harmful effects on plating range of carbonates are nullified. This is illustrated by the following bath:

Copper cyanide 10.0 Sodium cyanide 13.0 Free sodium cyanide 2.0 Potassium hydroxide 6.0 Zinc (as metal triethylenetetramine complex) 0.5

The bath was operated at F. with agitation with a bright plating range of 0-50 a.s.f. After the bath operated for a period of time it built up a concentration of sodium carbonate of about 8-10 ounces per gallon and the bright plating range was reduced to 0-20 a.s.f. Thereupon, 3 ounces per gallon of sodium nitrate were added and the bath operated under the same conditions. The bright plating range was increased to 0-75 a.s.f., substantially above the original range.

Example 9 Another standard brass plating bath known for some years had the following composition:

Copper cyanide 4.0 Zinc cyanide 2.8 Sodium cyanide 7.5 Free sodium cyanide 2.0 Sodium carbonate 4.0

The bath was operated at 75 -100 F. without agitation and had a brass plating range of 3-5 a.s.f. Upon the addition of 2 ounces per gallon of N0 in the form of potassium nitrite, the brass plating range was increased to 10 a.s.f.

Example 10 Another prior art brass plating bath is as follows:

Copper cyanide -a 12.0 Zinc cyanide 1.0 Sodium cyanide 13.7

Sodium hydroxide 8.0

It was operated at F. with agitation giving a brass deposit in the range of 35-100 a.s.f. When 4 ounces per gallon of N as ammonium nitrate was added, the range was increased to l a.s.-f.

Although the invention has been described setting forth a number of specific examples, the invention is not to be limited thereto as many variations may be introduced within the scope thereof. Other copper and brass plating baths may be modified to give the improved results described herein. in brass plating baths the zinc may be added as nitrate or nitrite, or as soluble salts of organic nitroso or nitro compounds. Other organic or inorganic nitro compounds than those specifically named are suitable, it being important that they be soluble in the baths employed.

In view of the above the invention is to be broadly construed and to be limited only by the character of the claims appended hereto.

We claim:

1. A method of operating alkaline cyanide copper and brass plating baths which comprises adding to such a bath during the plating operation a soluble compound containing a radical taken from the class consisting of N0 N0 and NO, and electroplating articles therewith without intermediate filtration of insoluble matter, the ratio of copper to said radical being 0.l to 1, said soluble compound being added in sufficient amount to cause the bright plating range of said bath to be substantially increased.

2. A method of operating alkaline cyanide copper and brass plating baths which comprises adding to such a bath during the plating operation a soluble compound containing a radical taken from the class consisting of N0 N0 and NO, and electroplating articles therewith without intermediate filtration of insoluble matter, the ratio of copper to said radical being 0.1-10 to 1, said soluble compound being added in suflicient amount to cause the bright plating range of said bath to be substantially increased.

3. A method according to claim 1 in which the alkalinity of said bath is produced by sodium hydroxide.

4. A method according to claim 1 in which said soluble compound is the salt of a metal taken from the class consisting of copper, sodium, potassium, ammonium, Zinc and cobalt.

5 A method according to claim 1 in which said soluble compound is an organic compound.

6. A method according to claim 1 in which said soluble compound is the alkali metal salt of an aromatic acid.

7. An alkaline cyanide copper and brass plating bath including copper cyanide, alkali metal cyanide and alkali metal hydroxide, having incorporated therein a soluble compound containing a radical taken from the class consisting of N0 N0 and NO, the ratio of copper to said radical being O.l30 to 1, said soluble compound being added in sufficient amount to cause the bright plating range of said bath to be substantially increased.

8. An alkaline cyanide copper and brass plating bath including copper cyanide, alkali metal cyanide and alkali metal hydroxide, having incorporated therein a soluble compound containing a radical taken from the class consisting of N0 N0 and NO, the ratio of copper to said radical being 0.ll0 to 1, said soluble compound being added in sufficient amount to cause the bright plating range of said bath to be substantially increased.

9. A bath according to claim 7 in which said alkali metal is sodium.

10. A bath according to claim 7 in which there is present a substantial amount of alkali metal carbonate.

References Cited in the file of this patent UNITED STATES PATENTS Benner et a1. Jan. 6, 1948 Stareck Mar. 16, 1948 OTHER REFERENCES 

1. A METHOD OF OPERATING ALKALINE CYANIDE COPPER AND BRASS PLATING BATHS WHICH COMPRISES ADDING TO SUCH A BATH DURING THE PLATING OPERATION A SOLUBLE COMPOUND CONTAINING A RADICAL TAKEN FROM THE CLASS CONSISTING OF NO3, NO2, AND NO, AND ELECTROPLATING ARTICLES THEREWITH WITHOUT INTERMEDIATE FILTRATION OF INSOLUBLE MATTER, THE RATIO OF COPPER TO SAID RADICAL BEING 0.1-30 TO 1, SAID SOLUBLE COMPOUND BEING ADDED IN SUFFICIENT AMOUNT TO CAUSE THE BRIGHT PLATING RANGE OF SAID BATH TO BE SUBSTANTIALLY INCREASED. 